Gas sensor

Abstract

A gas sensor (100) extending in an axial direction AX including: a gas sensor element (120) which detects the concentration of a specific gas in a gas under measurement; a tubular metallic shell (110) having a polygonal tool engagement portion (110B) surrounding the gas sensor element (120); a tubular outer tube (103) which extends rearward from the metallic shell (110), surrounds the gas sensor element (120), and has an opening (103E) at a rear end thereof; a sealing member (191) which seals the opening (103E); and a tubular heat dissipating member (104) which surrounds the outer tube (103) and reduces the amount of heat transferred from the forward end side of the gas sensor (100) through the outer tube (103) to the sealing member (191). The maximum diameter D1 of the heat dissipating member (104) is equal to or less than the opposite side dimension D2 of the tool engagement portion (110B).

What is claimed is: 
     
       1. A gas sensor extending in an axial direction and comprising:
 a gas sensor element which detects the concentration of a specific gas in a gas under measurement; 
 a tubular metallic shell having a polygonal tool engagement portion surrounding the gas sensor element; 
 a tubular outer tube which extends rearward from the metallic shell, surrounds the gas sensor element, and has an opening at a rear end thereof; 
 a sealing member which seals the opening; and 
 a tubular heat dissipating member which surrounds the outer tube and reduces the amount of heat transferred from a forward end side of the gas sensor through the outer tube to the sealing member, 
 wherein a maximum diameter of the heat dissipating member is equal to or less than an opposite side dimension of the tool engagement portion, which is a distance between two opposite sides of the tool engagement portion, and 
 the outer tube is in direct contact with the metallic shell. 
 
     
     
       2. The gas sensor as claimed in  claim 1 , wherein a rear end of the heat dissipating member is located forward of a forward end of the sealing member or wherein the heat dissipating member at least partially overlaps the sealing member in the axial direction and is spaced apart from the outer tube in at least part of a region in which the heat dissipating member overlaps the sealing member. 
     
     
       3. The gas sensor as claimed in  claim 1 , wherein the outer tube has a heat transfer resistance per unit length in the axial direction that is larger than that of the heat dissipating member. 
     
     
       4. The gas sensor as claimed in  claim 1 , wherein the heat dissipating member has a thickness that is larger than the thickness of the outer tube. 
     
     
       5. A gas sensor as claimed in  claim 1 , wherein the metallic shell has a mounting portion extending rearward from a rear end of the tool engagement portion, and the heat dissipating member is fixed to the mounting portion directly or indirectly through the outer tube while overlapping the mounting portion in the axial direction. 
     
     
       6. The gas sensor as claimed in  claim 5 , wherein a forward end of the heat dissipating member, a forward end of the outer tube, and the mounting portion are integrally fixed by welding.